My Christmas Murder Mystery Book has been on hold since 2014!!! I NEED GUIDANCE ON HOW TO MYSTERY!

My murder mystery We Wish You A Bloody Christmas has been in the works since I came up with idea in 2010 (5th grade). Been on hold since 2014 due to not knowing to tie in all the things I want to do. Since then I’ve written easier things. I’ve proven good at decent plot twists, character development, motive, and plot. I’ve done soft fantasy, paranormal, even regular thrillers. Yet, doing a genre that specifically requires mystery and suspense to be the main factor of the book has somehow blocked my ability to continue writing it. My plot is such a good idea and I even planned the prequel better than the main story. All you mystery writing people, I need help. I don’t know where to start, so any questions?

When I’m stuck I listen to favorite music for 15 minutes or so.(through headphones) You know, the great singers, instrumentalists, etc. I listen to appreciate their amazing talents. How can a human being sing/play like that? I think. I just listen and enjoy. This gets my right brain out of the way and ideas with clear pictures roll out much easier.
Remember if you don’t write something bad… you’ll never write something good! SO WRITE!